Microwave dielectric spectroscopy is a technique that uses a microwave signal to measure properties of a dielectric material. When the microwave signal is applied to the dielectric material it creates an electromagnetic field that propagates through the dielectric material. Dielectric properties of a material are determined by the material's molecular structure, and properties of the material can be deduced by observing the propagation of an electric field through it. Dielectric spectroscopy is an attractive way to evaluate a material because it can provide a real-time indication of the material's properties and is non-destructive. Dielectric spectroscopy is used in a variety of applications including materials measurement, tomography, and process control, including monitoring chemical and biological reactions.
Two challenges in dielectric spectroscopy are guiding and monitoring the propagation of the electric field, as the energy from the electric field must be reliably and repeatedly contained and monitored. An important consideration in designing a microwave dielectric spectroscopy technique is the frequency dependence of the measurement, and it is often important to measure the dielectric properties of a material at different frequencies or over a wide frequency range. Unfortunately, many microwave dielectric spectroscopy probes only operate over a limited frequency range.
Microwave dielectric spectroscopy probes based on a coplanar waveguide structure that relies on the proximity to or incorporation of the dielectric material being measured offer board-band operation. However, most of the electromagnetic energy is coupled into the substrate of the coplanar waveguide. This reduces the sensitivity of the measurement.
A microwave dielectric spectroscopy probe that provides broad-band performance and high sensitivity is desirable.